1. Technical Field
The present invention relates, generally, to microelectronic devices and, more particularly, to methods for controlling power supply transients.
2. Background Information
Recent advances in digital integrated circuits have dramatically increased the speed and density of such circuits, giving rise to many challenges related to, among other things, degradation in waveform quality. In particular, as clock rates and circuit density increase, a significant amount of transient current must be supplied to charge and discharge the internal capacitive load of each signal. These severe current transients, if not adequately filtered or regulated, result in supply and ground xe2x80x9cbouncexe2x80x9d and, consequently, introduce bit errors into the digital logic through degraded noise margin and supply-induced timing violations.
Prior art methods for controlling transient current requirements are unsatisfactory in a number of respects. For example, it is known that supply and ground bounce can be mitigated through the use of voltage regulation, internal and external capacitive bypassing, and low-inductance and/or low-resistance pins. However, there are fundamental limits on how much regulation and bypassing can be performed before negatively impacting system cost and complexity.
FIG. 1 depicts a prior art circuit requiring current compensation. Specifically, the supply voltage 102 passes through a voltage regulator 104. Dynamic load 112 is connected in parallel with a bypass capacitor 110 to the voltage regulator via supply inductor 106 and ground inductor 108. A compensating current may be provided to dynamic load 112 such that the droop or spike amplitude during a transient event can be minimized until the external regulator 104 can accommodate the change in load current. If the compensating current can be made to exactly match the change in dynamic load 112, and can be applied without delay, then, in theory, the transient current experienced by dynamic load 112 can be cancelled and the droop or spike can be eliminated. In practical implementations, however, the current amplitude and duration will not exactly match, and there will be a significant delay from when the change in dynamic load is sensed and when the compensating current can be applied.
One approach to matching the current amplitude and duration is to use closed-loop control of the current generator. In this approach, either the net dynamic load or supply voltage is monitored and feedback is used to set the current compensation. This approach suffers from many drawbacks. For example, in order for a closed-loop arrangement to be stable, the bandwidth of the loop must be limited such that the loop stability criteria can be met. This results in a relatively slow response to transients and little if any suppression of the critical high frequency components.
Systems and methods are therefore needed to overcome these and other limitations of the prior art.
The present invention overcomes the limitations of the prior art by providing a system for supplying current to a dynamic load subject to transient current requirements. In accordance with one embodiment of the present invention, one or more sense units coupled to the dynamic load are configured to sense the rate of change of supply current required by the dynamic load during a transient event. One or more current sources coupled to the sense unit are configured to supply a current pulse to the dynamic load in response to the sense unit determining that the rate of change of supply current (di/dt) exceeds a predetermined threshold. The current pulse preferably has a shape characterized by a first region and a second region subsequent to the second region, wherein the first region includes a relatively low-duration first boost current which exceeds the transient current requirement, and wherein the second region includes a longer-duration second boost current which is less than the transient current requirement.
In accordance with another aspect of the present invention, a wideband transient suppression system includes a primary regulator configured to compensate for low frequency transients, and a secondary regulator configured to provide short-term compensation current to the dynamic load until the relatively slow primary regulator can accommodate the transient event. The secondary regulator includes two major functional blocks: a closed-loop voltage-sensing compensation circuit configured to compensate for transients falling within a mid-range frequency range, and an open-loop di/dt-sensing compensation circuit configured to compensate for transients falling within a high-frequency range.
In accordance with another aspect of the present invention, the first region of the current pulse is the result of an open-loop response to transient current requirements.
In accordance with another aspect of the present invention, the second region of the current pulse is the result of a closed-loop response to transient current requirements.
In accordance with an alternate embodiment of the present invention, multiple sense units and current sources are provided, each having associated delay times and/or thresholds.